> ## Documentation Index
> Fetch the complete documentation index at: https://docs.foldset.com/llms.txt
> Use this file to discover all available pages before exploring further.

# FastAPI

> Add Foldset payment gating to your FastAPI application

## Install

<CodeGroup>
  ```bash pip theme={null}
  pip install foldset-fastapi
  ```

  ```bash uv theme={null}
  uv add foldset-fastapi
  ```

  ```bash poetry theme={null}
  poetry add foldset-fastapi
  ```
</CodeGroup>

## Setup

<Steps>
  <Step title="Get your API key">
    Copy your API key from the [Foldset dashboard](https://foldset.com/dashboard/api-keys).
  </Step>

  <Step title="Set the environment variable">
    The SDK reads your API key from the `FOLDSET_API_KEY` environment variable.

    **Local development:** add it to a `.env` file and load it with [python-dotenv](https://pypi.org/project/python-dotenv/) or your preferred env loader. Make sure `.env` is in your `.gitignore`:

    ```
    FOLDSET_API_KEY=sk_live_...
    ```

    **Production:** set it in your hosting provider's environment variable settings (e.g. Railway, Render, AWS). Never commit API keys to your repository.
  </Step>

  <Step title="Add the middleware">
    ```python theme={null}
    import os
    from fastapi import FastAPI
    from foldset_fastapi import FoldsetMiddleware, FoldsetOptions

    app = FastAPI()

    # Add Foldset middleware
    app.add_middleware(
        FoldsetMiddleware,
        options=FoldsetOptions(api_key=os.environ.get("FOLDSET_API_KEY", "")),
    )

    # Your routes
    @app.get("/api/data")
    async def get_data():
        return {"message": "This content is protected"}
    ```

    The middleware must be added **before** your route handlers are registered. It will intercept requests that match your configured rules.
  </Step>

  <Step title="Configure routes">
    Head to the [rules page](https://foldset.com/dashboard/rules) to choose which paths to protect and set prices.
  </Step>
</Steps>

## How it works

The Foldset middleware runs on every incoming request:

1. Checks the request path against your configured rules
2. If no payment is required, the request passes through to your route handler
3. If payment is required and no valid x402 payment header is present, returns a `402 Payment Required` response with payment instructions
4. If a valid payment is attached, the request passes through and settlement completes after your route handler responds

### MCP server protection

If your FastAPI app hosts an MCP server (Streamable HTTP), Foldset can gate individual tool calls and resource reads. Configure MCP rules in the dashboard by specifying the endpoint path, method, and tool or resource name. Discovery methods like `tools/list` pass through for free with payment metadata attached.

## Update your robots.txt

Once Foldset is active, you want AI agents visiting your site so they can pay for access. If your `robots.txt` blocks AI crawlers, remove those rules. Foldset handles gating at the payment layer.

```
# Remove rules like these:
User-agent: GPTBot
Disallow: /

User-agent: ClaudeBot
Disallow: /
```